1. Field of Invention
The present invention relates to the general field of psychoacoustics which is defined, for purposes of this application, as the neuropsychological response of the brain to music. Specifically, the invention relates to a method and apparatus for translating an electroencephalographic (EEG) signal into specifically engineered music, feeding back that music to a selected area of the brain, via the ear, from which the EEG signal was generated so as to induce and control a wide variety of psychological and physiological states. The invention uses a new type of biofeedback music. The principles controlling the generation of this biofeedback are henceforth known as neuroacoustics.
2. Description of related knowledge
The human brain exhibits periodic electrical activity, also known as brain waves, at the microvolt level in discrete frequency ranges. This brain wave activity has traditionally been classified by frequency as follows: alpha waves lie in the frequency range of 8 to 13 Hz, beta waves lie in the frequency range of 13 to 28 Hz, and theta waves lie in the frequency range of 4 to 8 Hz. The brain also exhibits delta waves during sleep which are characterized by a relatively high amplitude and very low frequency, typically less than one complete cycle per second. Beta waves have a relatively low amplitude and correspond to a high level of arousal or anxiety. The brain is known to produce primarily alpha waves when a person is in a state of rest and relaxation. Theta waves are often associated with pre-sleep, dream-like mentations and visual imagery.
It is also known that EEG activity, muscular activity and other physiological measures may be modified with "biofeedback". Conventional biofeedback involves converting some measurable physiological activity of an individual into a feedback signal comprising an auditory or visual stimulus. The feedback signal provides the individual with an indication of his or her physiological activity. One type of biofeedback apparatus converts alpha waves into an audible tone that has a volume or pitch corresponding to the average level of alpha wave activity. Some individuals can alter their internal emotional state and relax by learning to alter the feedback signal.
Conventional biofeedback, however, has well known limitations. Most individuals require multiple sessions with a trained therapist to learn to adjust their brain wave activity in response to the feedback signal. Biofeedback can be tiresome and boring when the feedback signal has no interesting or pleasing qualities. Some studies have found that conventional biofeedback is so mechanistically routine that the feedback signal does not induce an effect unless a therapist is present to add emotional content and direction to the experience.
The feedback signal normally indicates only a time average of the relevant physiological activity. As such, conventional biofeedback provides an information pathway by which the brain is made consciously aware of the physiological activity. The feedback signal, however, has no direct effect on ongoing physiological activity and therefore cannot produce a true real time cybernetic feedback loop. U.S. Pat. Nos. 3,978,847 and 4,031,884 to Fehmi et al disclose a multiple channel phase integrating biofeedback computer that generates a feedback signal having a tone whose volume rises and falls with the rise and fall of the voltage in subsequent cycles of a brain wave train such as an alpha burst. The therapist or individual using the biofeedback computer may adjust a phase shift network to shift the phase of the feedback signal relative to the user's brain wave activity in accord with personal experience or personal preference. This feedback signal, however, does not appear to actively promote brain wave activity, nor does the feedback tone have musical or emotional content. Hence, the exact phase relationship of the feedback signal to the brain wave activity is not specified and does not appear to be critical to the proper functioning of the biofeedback computer.
Various approaches have been proposed to overcome the inadequacies of conventional biofeedback. One method for promoting relaxation is to play prerecorded complex sounds or colors which are at least not annoying and perhaps even psychologically enjoyable. The prerecorded sounds or colors may or may not be controlled by some measured physiological quantity. The feedback, however, does not communicate current, ongoing physiological activity, nor does the feedback induce or reinforce a physiological response. Rather, the feedback signal remains only an aid to learning which permits a person to learn to adjust his or her physiological activity.
Composers such as David Rosenboom and Alvin Lucier have incorporated EEG signals into musical compositions. These efforts have produced music that is interesting from an aesthetic perspective. The EEG signals are obtained from electrodes that are placed on the scalp without regard the physiological significance of the area of the brain that is producing the EEG activity. It is not surprising, therefore, that these musical composers have neither attained a real time physiological feedback loop nor advanced a workable methodology for attaining such an end.
Thomas Mullholland and Benard Turskey have criticized conventional biofeedback because the biofeedback signal communicates exclusively learning information. They maintain that the biofeedback signal should incorporate principles of engineering and cybernetics. Specifically, the feedback signal should be multidimensional and contain information about many features of the physiological response of interest. Further, the return of the feedback signal to the biological system of origin should be controlled so as to directly encourage and reinforce a desired physiological response. This criticism of conventional biofeedback is well taken. However, no known biofeedback device can induce a physiological response consistent with the procedural objectives proposed by Mullholland and Turskey.
Neurophysiologists know how to induce neural activity in the human brain using external stimuli. Sound is particularly useful stimulus because much of the cerebral cortex is sensitive to acoustical stimulation. Large scale neural activity may be induced in response to a variety of sounds. For example, the cortical electroencephalogram is particularly responsive to punctate sounds such as those produced by a drum or bell. The "evoked potential" phenomenon uses punctate sounds to periodically stimulate the brain. The brain eventually responds to the stimulation by producing brain wave activity at the same frequency as the stimulus. The punctate sound "drives" the brain to produce brain wave activity at the frequency selected by the neurophysiologist. A flashing light is sometimes used as an alternate form of stimulation or as a supplement to the acoustical stimulation.
The physiological stimulation associated with the evoked potential becomes unpleasant if continued for a period of time. Indeed, an evoked potential session becomes particularly unpleasant when uninteresting, regularly occurring stimuli are used to synchronously drive the EEG at a particular frequency. This unfavorable psychological response appears to result, at least in part, from the inability of the brain to control the external stimulus.
Musicians know how to give sound a form, content and direction that is both interesting and emotionally moving to a listener. Such sounds are commonly known as music. The ability of music to produce an emotional response has been known for many centuries in cultures throughout the world. Only recently, however, have psychologists and musicians begun to codify the principles that govern the emotional response to music or to exploit this knowledge with newly developed methods of precise music synthesis.
Music typically has not been used to evoke controlled responses in the brain nor has the feedback signal produced by conventional biofeedback devices been specifically organized into musical form. This is surprising since musicians know how to make sound convey many levels of meaning. The art has yet to appreciate the utility of music to induce particular, selectable forms of neural activity. This failure stems, at least in part, from a perceived dissimilarity in goals between the fields of music and psychophysiology. Further, the basic principles governing the unique neurological, physiological and emotional effects which music can induce when used systematically in a real time cybernetic biofeedback loop have no precedence in the art.